1. Field of the Invention
The present invention relates to an ink jet recording head and a producing method therefor, and more particularly to a surface shape of an ink supply aperture.
2. Related Background Art
The ink jet recording method is rapidly becoming popular in recent years, owing to its advantages of negligibly low noise when recording, an ability for achieving a high-speed recording and an ability of fixing a recording on so-called plain paper without any particular process.
Among ink jet recording heads, a head in which an ink droplet is discharged perpendicularly to a substrate bearing an ink discharge energy generating element is called a “side shooter recording head”, and the present invention relates to an ink supply in such a side shooter recording head.
There will now be explained a general structure of such a side shooter recording head.
FIG. 7 is a schematic perspective view showing a common side shooter ink jet recording head, and FIG. 8 is a cross-sectional view along an ink path of the recording head shown in FIG. 7.
The side shooter ink jet recording head shown in FIGS. 7 and 8 is prepared by forming, by a film forming technology on a silicon substrate, a discharge energy generating portion, a common ink chamber, an ink path, a discharge port 25, etc. to be explained later. In a silicon substrate having such components (device substrate 27), there is formed a penetrating ink supply aperture 29 of an elongated shape. On both sides of the ink supply aperture 29, plural electrothermal converting members 30 are formed at a predetermined pitch in two rows with a mutually displaced relationship by a half pitch, along a conveying direction of a recording material, namely along a longitudinal direction of the ink supply aperture 29, thereby respectively constituting discharge energy generating portions. The device substrate 27 is provided, in addition to such electrothermal converting members 30, with electrode terminals 31 for electrical connection of the electrothermal converting members 30 with a main body of the apparatus and electric wirings (not shown), by a film forming technology. On the device substrate 27, there is formed an orifice plate 33 provided with a common ink chamber 32 communicating with the ink supply aperture 29, plural discharge nozzles 25 respectively opposed to the electrothermal converting members 30, and ink paths 34 communicating with the common ink chamber 32 and the respective discharge nozzles 25. A partition wall 35 is formed between adjacent ink paths 34.
A liquid supplied from the ink supply aperture 29 to each ink path 34 causes, in response to a drive signal applied to the electrothermal converting member 30 corresponding to the ink path 34, boiling by heat generation in the electrothermal converting member 30, and is discharged from the discharge nozzle 25 by a pressure of a thus generated bubble.
In such side shooter recording head, an ink supply for the ink droplet discharge is achieved by forming a penetrating aperture in the substrate (device substrate) bearing an electrothermal converting element serving as a discharge energy generating element.
For forming an ink supply aperture in the device substrate of such ink jet recording head, there has been proposed a method utilizing drilling, laser or sand blasting, or a method of utilizing anisotropic etching as described in Japanese Patent Application Laid-open No. H09-11479.
Also, Japanese Patent Application Laid-open No. 2003-53979 proposes a method of etching a portion exposed on a first surface of the substrate, then coating an etched portion of the substrate and repeating these steps alternately until a fluid channel is formed through the substrate. Such a method is called a Bosch process.
However, an ink supply aperture formation by drilling, laser or sand blasting involves a difficulty that a dimensional precision of the ink supply aperture is difficult to obtain.
Also in case of an ink supply aperture formation by an anisotropic etching, the ink supply apertures will have a trapezoidal cross section (cf. FIG. 8) in case of a silicon substrate of <100> orientation. Therefore, in case of producing a chip for an ink jet recording head with a silicon substrate of such crystalline orientation, it is difficult to reduce the size of such chip whereby a cost reduction becomes very difficult. On the other hand, an ink supply aperture perpendicular to the substrate surface can be obtained in case of a silicon substrate of <110> orientation. However, because such <110> substrate shows a smaller ON-resistance in a semiconductor circuit prepared thereon, a chip size reduction is limited in comparison with a case with the <100> silicon substrate.
Also, an ink supply aperture formation by a Bosch process can provide a substantially vertical ink supply aperture, having a highly precise aperture width and a high aspect ratio. However, repetition of etching steps and deposition steps results in an undulating shape, called scallop pattern, similar to that observed on a scallop shell and as shown in FIG. 1. A depth a of the scallop pattern shown in FIG. 1 corresponds to an amount of side etch in an etching step. Also, a distance b between adjacent projecting points of the scallop pattern corresponds to an etch amount in the etching step, and the amounts a and b are both influenced by an aperture rate of the pattern on the wafer surface, a pattern size and an etching condition.
On the other hand, when an ink supply aperture is formed by a dry etching in a silicon substrate, a silicon crystal face exposed on a lateral wall of the ink supply aperture is not necessarily a (111) plane showing a low etching rate for an alkaline solution. Consequently, in case an alkaline ink is employed in an ink jet recording head having such ink supply aperture, silicon dissolves into the ink. It is therefore necessary to cover the surface with a film resistant to the alkaline ink. However, in case the scallop pattern formed on the etched lateral wall of the ink supply aperture shows significant projections and recesses, it becomes difficult to obtain a sufficient coverage for example on a projecting point of such scallop pattern, as indicated by a circle in FIG. 2. A thicker coating can achieve a sufficient coverage even on such point, but a precise aperture width becomes difficult to obtain in the ink supply aperture. A fluctuation in the width of the ink supply aperture results in a fluctuation in a distance from an end of the ink supply aperture to the electrothermal converting element (heater). Thus, a flow resistance may fluctuate among the nozzles, and an anticipated refill frequency (repeating rate per unit time of a liquid refilling in the liquid flow path after a liquid discharge from the discharge port) may become unattainable.